Women launching fitness efforts can quickly be overwhelmed with negative feelings if they reflect on their image, a study shows. Chances of success are all that get slimmer.

Nelida Willoughby took a hard look at herself in the mirror a year ago -- and what she saw hit her like a sledgehammer.

"I couldn't believe that was me," says the 41-year-old Woodland Hills marketing executive. "It was a jolt seeing my reflection. I had to ask myself, 'How have I neglected myself to the point where I look like this now?' When I finally stepped out of the black hole, I said, 'I have to do something to be better.' Then, for me, the mirror had to disappear for a while."

Today, Willoughby is an avid exerciser who is 24 pounds lighter and many inches around smaller -- and the decision to step away from the mirror might just be the reason why, suggests a new study from McMaster University in Hamilton, Ontario, Canada.

Sedentary women who exercised for 20 minutes in front of a mirror felt less energized, less positive and upbeat than women who worked out without a mirror. Those who exercised without the mirror also didn't report being physically exhausted at the end of their workout, the Canadian researchers found.

Kathleen Martin Ginis, a professor of kinesiology at McMaster who headed the research project, and colleagues studied 58 college-age women who exercised less than 15 minutes a week.

"Mirrors make us more self-aware, and when that happens, we evaluate ourselves and how we ideally think we should be," says Martin Ginis.

She says she was surprised to find that all the women reported negative feelings in front of a mirror, irrespective of whether their body image was good or bad before they began.

"We're not just evaluating how we look. We start to evaluate ourselves on everything in our lives -- how good a cook we are, how we have done in our careers, our love life failures, even how poorly we did years ago on some math test in junior high," says Martin Ginis.

Heather Krell, an assistant clinical psychiatrist at the UCLA Neuropsychiatric Institute, explains that people's relationships with the mirror often change for the worse during adolescence as they watch the alterations that puberty can bring.

"So here we all are, still comparing ourselves from back in our early teens, and then we are in a world where increasingly we are measuring ourselves against idealized images in the media that no one can ever live up to," says Krell. "One perceived inadequacy leads to another, and another and another."

If mirrors in a gym prompt some women to mentally add up life's failures, it's little wonder so many people don't stick to a fitness program.

Gary Heavin, founder of Curves, a Waco, Texas-based chain of no-frills fitness clubs for women only, suggests that gym decor may play some role in the fact that about 70% of American women don't exercise regularly. At Curves, which provides circuit-training exercise programs, mirrors aren't used in the gym design.

"Gyms were initially designed for men," says Heavin. "When my wife and I opened the first Curves in '91, we were conscious of the comfort that women had when they didn't have to look at themselves -- or have men looking at them while they exercised."

Mirrors aren't necessarily always detrimental, Martin Ginis cautions -- far from it. Her study found that beginning exercisers -- in this case, young college-age women -- were negatively affected by mirrors, but more research is needed to determine if those findings apply to a broader range of women.

"Mirrors are helpful, and are very beneficial for checking your form and seeing progress," she says. "In fact, we know from other studies that experienced women in the gym actually feel more confident when they can see their workouts. They start using the mirror for something functional."

She recommends women begin exercise by walking, cycling or joining a gym without mirrors. Since mirrors are a feature of so many gyms, women might consider exercising at home initially until they feel more comfortable about their bodies and workouts.

That makes sense to Willoughby, who kick-started her fitness regime a year ago by walking and riding a bike around her neighborhood and now regularly works out with a private trainer at a Calabasas gym. "Now I look at the muscles that I have, the thighs that are each 5 inches smaller. The mirror isn't the measure, it just reinforces what I have given myself."